1. Field of the Invention
The present invention relates to an image forming apparatus which takes outside air into a housing to cool down the inside thereof.
2. Background Arts
In an image forming apparatus such as a printer, a copy machine, a facsimile and the like, there are provided many parts in a housing some of which generate heat. In a color thermal printer in which a thermal head makes tightly contact with a color thermo-sensitive recording paper for thermal recording, for example, a greatest amount of heat is generated from an optical fixing lamp. The fixing lamp fixes the thermal coloring layer of the color thermo-sensitive recording paper. When the bulb temperature of the fixing lamp increases too much, the efficiency of fixing decreases due to decrease in an amount of light emitted therefrom. In the thermal head, a heat element generates heat to form pixels on the thermo-sensitive recording paper, so that the recording density of the color pixels is varied as the temperature of the thermal head increases. Therefore, it is necessary to control the temperature inside the housing of the color thermal printer.
There is known an image forming apparatus which can efficiently cool down the inside of the housing. The image forming apparatus has a duct for discharging the heat inside of the housing into the outside, and a fan for generating airflow inside the duct. Japanese Patent Laid-Open Publication No. 2000-305439, for example, discloses an image forming apparatus having plural discharge fans installed inside a duct in series. A louver of the duct is connected to the inside and outside of a housing. The discharge fans discharge heat generated inside the housing with outside air from a discharge opening connected to the outside of the housing. An image forming apparatus, disclosed by Japanese Patent Laid-Open Publication No. 08-220952, further blows the outside air sucked from the outside of the housing on a heat source to cool it down.
In an image forming apparatus with plural heat sources, as described in Japanese Patent Laid-Open Publications No. 06-059549 and 2002-023571, a duct is so disposed inside the housing as to pass the vicinity of each heat source. An opening is formed in the duct at a position so as to face each heat source. A discharge fan installed inside the duct discharges heat generated from the heat sources into the outside of the housing.
In the above image forming apparatuses, however, dust in the outside air is sucked thereinto with the outside air. The dust tends to cause smudges on a recording paper, so that a print image is adversely affected. For this reason, the image forming apparatuses according to Japanese Patent Laid-Open publications No. 08-220952 and 2002-023571 further comprise an air filter provided inside the duct to eliminate the dust. In these image forming apparatuses, it is possible to prevent degradation in the print image, because the dust in the outside air does not get into the apparatus.
When the air filter disposed inside the duct is clogged with the dust, however, an amount of airflow rapidly decreases. Cooling effect inside the housing extremely becomes worse. Thus, the air filter needs troublesome maintenance, in other words, needs to be exchanged at regular intervals.
In the image forming apparatus according to Japanese Patent Laid-Open publication No. 2002-023571, a switch valve is provided in some of plural discharge openings disposed in a discharge path. Since the switch valve opens and closes in accordance with the clogging of the air filter, it is possible to prevent decrease in the amount of the airflow for discharging. In this image forming apparatus, air filtered by the air filter passes through the discharge openings. Accordingly, in a case where the air filter heavily clogs, the airflow cannot be generated in the discharge path even if the switch valve is opened.
An object of the present invention is to provide an image forming apparatus which can cool the inside of a housing even when an air filter clogs.
To achieve the above object, an image forming apparatus with a housing according to the present invention comprises a duct provided in the housing, an air filter, an inside inlet, and a cooling fan. The duct has at least one outside inlet opened to the outside of the housing, and at least one discharge opening provided in the housing. The air filter is disposed between the outside inlet and the discharge opening. The inside louver sucks inside air in the housing. The cooling fan is disposed in front of the discharge opening of the housing. The air filter filters outside air sucked into the duct, to prevent dust from getting into the housing. The cooling fan releases mixed air, which includes the outside air entered from the outside inlet and passing through the duct, and the inside air entered from the inside inlet, into the housing, for the purpose of circulating the air inside the housing.
The inside inlet may be a gap formed between the discharge opening and a cooling fan, or may be at least one opening formed in a sidewall of the duct. The opening is formed between the air filter and the cooling fan.
The cooling fan blows the mixed air on a part generating heat to cool it.
A suction fan may be provided in the vicinity of the outside inlet. The suction fan forcefully takes the outside air into the duct through the outside inlet.
The suction fan may be disposed between the outside inlet and the air filter.
The operation of the cooling fan and the suction fan is so controlled by a common controller that the cooling fan and the suction fan rotate in the same timing.
According to the present invention, the air circulates inside a housing even when an air filter clogs, because the image forming apparatus is provided with an inside inlet for sucking inside air in the housing. The air is blown on a part generating heat in the housing, so that it is possible to cool the inside of a housing even when an air filter clogs. It is also possible to contribute to reduction in cost of the image forming apparatus, as the number of the controllers decrease.